The present invention relates to the field of fuser members useful in electrophotographic copying.
A widely used method for affixing toner materials to a receiver sheet is by the application of high temperature and pressure in the fusing subsystem of a photocopying machine. A common configuration for a fusing subsystem is to place a pair of cylindrical rollers in contact. The roller that contacts the side of the receiver sheet carrying the unfixed or unfused toner is known as the fuser roller. The other roller is known as the pressure roller. The area of contact is known as the nip.
A toner receiver sheet containing the unfixed or unfused toner is passed through the nip. A soft coating on one or both of the rollers allows the nip to increase in size relative to the nip which would have been formed between two hard rollers and allows the nip to conform to the receiver sheet, improving the fusing quality. Typically, one or both of the rollers are heated, either through application of heat from the interior of the roller or through external heating. A load is applied to one or both rollers in order to generate the higher pressures that are necessary for good fixing or fusing of the toner to the receiver sheet.
The application of high temperature and pressure as the receiver sheet passes through the nip causes the toner material to flow to some degree, increasing its contact area with the receiver sheet. If the cohesive strength of the toner and the adhesion of the toner to the receiver sheet is greater than the adhesion strength of the toner to the fuser roller, complete fusing occurs. However, in certain cases, the cohesive strength of the toner or the adhesion strength of the toner to the receiver is less than that of the toner to the fuser roller. When this occurs, some toner will remain on the roller surface after the receiver sheet has passed through the nip, giving rise to a phenomenon known as offset. Offset can also occur on the pressure roller.
Offset is undesirable because it can result in transfer of the toner to non-image areas of succeeding copies and can lead to more rapid contamination of all machine parts in contact with the fusing rollers and to increased machine maintenance requirements. It can also lead to receiver (paper) jams as the toner-roller adhesion causes the receiver sheet to follow the surface of the roller rather than being released to the post-nip paper path.
It is common in some machines to apply release oil externally to the roller in the machine as it is being used. The release oil is typically poly(dimethylsiloxane) (PDMS) oil. PDMS oil does an excellent job in its role as release agent; however, there are associated disadvantages.
The release agent can be spread to other parts of the machine, causing contamination. Further, streaks may appear in the image as a result of imperfect spreading of the release agent across the roller surface. Therefore, it is desirable to improve the release performance of the roller materials in order to be able to minimize the amount of release agent that must be applied to the roller.
The release agent""s compatibility with PDMS-based roller materials result in swelling of the rollers. This swelling cannot be easily compensated for, since it is generally non-uniform. Paper passing over the rollers can wick away some of the release oil within the paper path, resulting in a differential availability of the release oil to roller areas within and outside the paper path. This causes differential swell of the roller inside and outside the paper path so that a xe2x80x9cstep patternxe2x80x9d is formed in the roller. This can cause problems when different size papers are used and can lead to increased wear and decreased roller life as described in U.S. Pat. No. 5,753,361. This wear can also lead to an uneven pressure distribution between the two rollers of the fusing assembly resulting in poor print quality as described in U.S. Pat. No. 5,035,950 and as is well known in the art. Another associated problem is the tendency of a silicone layer to soften as it swells with the polydimethylsiloxane release fluids and its subsequent debonding as described in U.S. Pat. No. 5,166,031. Here the suggested solution to the problems of the silicone fuser member coating was to develop fluoroelastomer analogs to replace the silicone. However, the toner""s tendency to offset is sacrificed.
Use of a soft fuser roller and a harder pressure roller have been shown to facilitate release of the toned receiver from the fuser roller. Low surface energy materials such as fluorine-containing coatings or silicone rubbers have been used as fuser roller coatings. An example of a low surface energy material is described in U.S. Pat. No. 3,731,358 which discloses the use of a poly(dimethylsiloxane) as a coating for a fuser roller. This patent also discloses coating the roller with silicone oil after it has been used for a period of time in order to restore release properties.
In European Patent Application 0 417 814 A, there is disclosed a fuser roller having a PDMS outer layer which has filler that contains absorbed silicone oil. It also discloses a fuser roller having a low viscosity PDMS oil incorporated therein in a comparative example. Poor offset performance was noted.
Addition of a low viscosity silicone oil into the roller material during formulation has also been suggested to improve the release properties of the roller in U.S. Pat. No. 4,074,001.
U.S. Pat. No. 5,654,052 describes a fuser member having as its outermost layer, a composite material comprising: a crosslinked, oxide filled poly(dimethylsiloxane) which contains and a non-crosslinked, non-reactive poly(dimethylsiloxane) oil having a viscosity of at least 25,000 CPS. The disadvantage of this being the poly(dimethylsiloxane) oil is not bound to the polymer resulting in poor toughness and wear as well as the oil being able to leach out of the fuser member. Thus limiting the amount of oil which can be incorporated oil to about 1%.
There continues to be a need for improved fuser and pressure rollers with improved fusing performance, e.g. increased toner release without reducing the toughness or drastically affecting the wear properties.
It is an object of the present invention to provide an improved fuser member with improved toner release.
In accordance with the present invention there is provided a fuser member having a support metallic core and a layer of material formed over the metallic core, the layer including composite material, comprising:
(a) a reactive crosslinkable poly(dialkylsiloxane);
(b) a cross-linked poly(dialkylsiloxane) incorporating an oxide, wherein the poly(dialkylsiloxane) has a weight average molecular weight before crosslinking of about 5,000 to 80,000; and
(c) one or more silane crosslinking agents.
An advantage of the present invention is that incorporating a high molecular weight reactive polyfunctional poly(C(1-6) alkyl)siloxane polymer causes an improvement in toner release of the fusing member.
Another advantage of the current invention is that it successfully increases the oil swell resulting in the advantages listed above without sacrificing the toughness and without significantly affecting the wear properties.
Another advantage of the current invention is that it permits incorporation of higher amounts of poly(dimethylsiloxane) than were nonreactive poly(dimethylsiloxane) oil to be incorporated.